piezoelectric effect piezo techlology tutorial pi ceramic

7/28/2019 Piezoelectric Effect Piezo Techlology Tutorial PI Ceramic

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Piezo Technology

l o n g

L

P EV

GND

P E

P E

P E

P EV GND

P E

P E

P E

P E

2,51,5 2,00,5 1,00,0

1500

1000

500

2000

0

EPP [kV/mm]

d ( G S )

[ p m / V ]

d15

PIC155 bipolar

d15

PIC255 bipolar

d33

PIC153 unipolar

d33

PIC151 unipolar

d33

PIC255 unipolar

d33 PIC252 unipolar

-d31

PIC252 unipolar

(1)

(2)

O2

Pb

Ti, Zr

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4

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Piezo TechnologyCOntEnts

Basic Principles o Piezoelectricity 35

Piezoelectric Eect, Ferroelectric Polarization, Expansion o the Polarized

Piezo Ceramic

Piezoelectric Actuator Materials 36

Piezoceramic Materials and Properties

Displacement Modes o Piezoelectric Actuators 37

Longitudinal Stack Actuators 37 – Shear Actuators, Picoactuator® 38

PT-Tube Tube Actuators 39 – Contracting Actuators 40 – Bending Actuators 41

Manuacturing o Piezo Actuators 42

Multilayer Tape Technology 42 – Pressing Technology 43

PT-Tube Tube Actuators, DuraAct 44

Properties o Piezoelectric Actuators 45

Displacement Behavior 45

Nonlinearity 45 – Hysteresis, Creep 46 – Position Control 47

Temperature-Dependent Behavior 48

Forces and Stinesses 50

Preload, Load Capacity, Stiness 50 – Force Generation and Displacement,

Typical Load Cases 51 – Actuator Dimensioning and Energy Consideration 53

Dynamic Operation 54

Resonant Frequency, How Fast Can a Piezo Actuator Expand?, Dynamic Forces

Electrical Operation 55

Electrical Behavior, Electrical Capacitance, Positioning Operation 55 – PowerConsumption o the Piezo Actuator, Heat Generation in the Piezo Element, Continuous

Dynamic Operation 56 Switching Applications, Pulse-Mode Operation 57

Ambient Conditions 58

Vacuum Environment, Inert Gases, Magnetic Fields, Gamma Radiation,

Environments with High Humidity, Liquids

Reliability o PICMA® Multilayer Actuators 59

Lietime when Exposed to DC-Voltage 59 – Lietime in Dynamic Continuous

Operation 60

Amplifer Technology: Piezo Electronics or Operating Piezo Actuators 61

Characteristic Behavior o Piezo Amplifers 61

Power Requirements or Piezo Operation, Amplier Frequency Response Curve,

Setting the Control Input Voltage

Solutions or High-Dynamics 24/7 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Switched Ampliers with Energy Recovery, Piezo Overtemperature Protection,

Valid Patents 62 – Linearized Ampliers or Piezo Displacement Without Hysteresis,

Charge Control, Charge and Displacement 63

Handling o Piezo Actuators 64

Mechanical Installation 64 – Electrical Connection, Sae Operation 65

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3


Longitudinal Stack Actuators

In longitudinal piezo actuators, the electric

eld in the ceramic layer is applied parallel

to the direction o polarization This induces

an expansion or displacement in the di-

rection o polarization Individual layers pro-

vide relatively low displacements In order

to achieve technically useul displacement

values, stack actuators are constructed,

where many individual layers are mecha-nically connected in series and electrically

connected in parallel (g 5)

Longitudinal stack actuators are highly

ecient in converting electrical to mechani-

cal energy They achieve nominal displace-

ments o around 01 to 015% o the actua-

tor length The nominal blocking orces are

on the order o 30 N/mm2 in relation to the

cross-sectional area o the actuator Values

o up to several 10,000 newton can thus be

achieved in the actuator

Longitudinal stack actuators are excellently

suited or highly dynamic operation due to

their high resonant requencies A mecha-

nical preloading o the actuator suppresses

dynamically induced tensile orces in

brittle ceramic material, allowing response

times in the microsecond range and a high

mechanical perormance

In addition to the expansion in the di-

rection o polarization, which is utilized

with longitudinal actuators, a contraction

always occurs in the piezo actuator that

is orthogonal to its polarization when it

is operated with an electric eld parallel

to the direction o polarization

This so-called transversal piezoelectric

eect is used by contracting actuators,

tube actuators, or bending actuators

Examples o longitudinal

stack actuators are the

multilayer piezo actuators

PICMA® Stack, Encapsu-

lated PICMA®, PICMA®

Chip, as well as the stack

actuators PICA Stack,

PICA Power, PICA Thru

that are glued together

rom individual plates,

and the crystalline Pico-

actuator®

ΔLlong

Longitudinal dis-

placement [m]

d33(GS)

Longitudinal

piezoelectric

large-signal deor-

mation coecient

[m/V]

n Number o

stacked ceramic

layers

V Piezo operating

voltage [V]

l o n g

L

P EV

GND

P E

P E

P E

P EV GND

P E

P E

P E

P E

Fig 5

ΔLlong

= n d33(GS)

V (Equation 1)

Piezoelectric Actuatorsd IsPlACEMEnt MOdEs



8


Shear Actuators

In piezoelectric shear actuators, the electric

eld in the ceramic layer is applied orthogo-

nally to the direction o polarization and the

displacement in the direction o polarization

is utilized The displacements o the indivi-

dual layers add up in stacked actuators here

as well (g 6)

The shear deormation coecients d15

are

normally the largest piezoelectric coeci-

ents When controlled with nominal volta-

ges, PIC ceramics achieve d15(GS)

values o up

to 2000 pm/V The permissible controlling

eld strength is limited in order to prevent

a reversal o the vertically oriented polari-

zation

When lateral orces act on the actuator, the

shear motion is additionally superimposed

by a bending The same eect occurs in

dynamic operation near the resonant re-

quency

Furthermore, shear stresses cannot be com-

pensated by a mechanical preload Both,

limit the practical stacking height o shear

stacks

Shear actuators combined with longitudinal

actuators yield very compact XYZ stacks

with high resonant requencies

Picoactuator® Technology

Picoactuator® longitudinal and shear actua-

tors are made o the crystalline piezoelectricmaterial PIC 050 The specic displacement

is ±002% (shear actuators) or ±001% (lon-

gitudinal piezo actuators) o the actuator

length and is thus 10 times lower than or

classic piezo actuators made o lead zirco-

nate - lead titanate (PZT) The displacement

here is highly linear with a deviation o only

02%

Fig 6

ΔLshear

= n d15(GS)

V (Equation 2)

Lshear

V

GND EP

A typical application or

shear actuators are drive

elements or so-called

stick-slip motors

Shear actuators rom PI

Ceramic are oered as

product lines PICA Shear

and Picoactuator

Fig 7:

Measured Nonlinearity o a Picoactuator®

Displacement Modes (Continued)

V GND

E

E

E

E

E

E

E

E

P

P

P

P

P

P

P

P

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0

Contracting Actuators

Typically, piezo contracting actuators are

low-prole components Their displacement

occurs perpendicularly to the polarization

direction and to the electric eld The dis-

placement o contracting actuators is based

on the transversal piezoelectric eect whe-

reby up to approx 20 µm is nominally achie-

ved

Multilayer elements oer decisive advan-

tages over single-layer piezo elements in

regard to technical realization: Due to the

larger cross-sectional area, they generatehigher orces and can be operated with a

lower voltage (g 11)

As a result o the contraction, tensile stres-

ses occur that can cause damage to the

brittle piezo ceramic A preload is thereore

recommended

For the patch actuators o the DuraAct pro-

duct group, a piezo contractor is laminated

into a polymer This creates a mechanical

preload that protects the ceramic againstbreakage (p 14)

Multilayer contracting actuators can be re-

quested as special versions o the PICMA®

Bender product line (p 13)

Fig 11

ΔLtrans

= d31 (GS)

l V (Equation 6)

h

ΔLtrans

E

E

E

E

P

P

P

P

GND V

EP

V

GND

i_ _ill i _ i .i . .

Displacement Modes (Continued)


ΔLtrans

Transversal dis-

placement [m]

d31(GS)

Transversal piezo-

electric large-sig-

nal deormation

coecient [m/V]

l Length o the

piezo ceramic in

the direction o

displacement [m]

h Height o a

ceramic layer [m]

n Number o

stacked ceramic

layers

V Piezo operating

voltage [V]

ΔLbend

Bending displace-

ment [m]

lf

Free bender

length [m] (p 12)

hp

Height piezo-

ceramic element

[m]

Rh

Ratio o the

heights o the

substrate (hs)

and piezoceramic

element (hp) in a

composite bender

(Rh=h

s /h

p)

RE

Ratio o the elas-

ticity modulus o

the substrate (Es)

and the piezocera-mic element (E

p)

in a composite

bender (RE=E

s /E

p)

V F

Fixed voltage or

bender actuator

control [V] (V and

VF

can be super-

imposed with an

oset voltage)

E

E

P

P

lf

hP

i_1 137_illu_ .in 1 . .1 1 :

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The more ne-grained the ceramic materi-

al used, the thinner the multiple layers that

can be produced In PICMA® Stack actua-

tors, the height o the active layers is 60 µm

and in PICMA® Bender actuators around 20

to 30 µm, so that the benders can be opera-

ted with a very low nominal voltage o only

60 V

Multilayer Tape Technology

The technologies or manuacturing pi-

ezo actuators decisively contribute to

their unction, quality and eciency

PI Ceramic is procient in a wide range o

technologies, rom multilayer tape techno-

logy or PICMA® stack and bending actua-

tors, through glued stack actuators or lon-

gitudinal and shear displacements, up to the

construction o crystalline Picoactuator® ac-

tuators, the DuraAct patch transducers and

piezoceramic tubes

PI Ceramic multilayer actuators, PICMA® or

short, are manuactured in large batches

with tape technology First, the inner elec-

trode pattern is printed on thin PZT tapes

while still unsintered and these are then

laminated into a multilayer compound In

the subsequent coring process, the cera-

mic and the inner electrodes are sintered

together The nished monolithic multilayer

piezo element has no polymer content any-

more

The inner electrodes o all PICMA® actuatorsare ceramically insulated (g 19) PICMA®

stack actuators use a patented structure

or this purpose, in which a thin ceramic in-

sulation tape covers the electrodes without

signicantly limiting the displacementFinal inspection

Assembly

Polarization

Application o the termination electrodes

Grinding, lapping

Debindering and sintering (coring)

Cutting and green shaping

Isostatic pressing

Stacking, laminating

Screen printing o the inner electrodes

Tape casting

Slurry preparation

Processing o the

piezo ceramic powder

Multilayer Tape Technology

Fig 19: In PICMA® stack actuators, a

ceramic insulation tape covers the

inner electrodes

Hermetically encapsulated PICMA® were developed

or applications in extremely high humidity and in

rough industrial environments They are equippedwith corrosion-resistant stainless-steel bellows, inert

gas lling, glass eedthroughs and laser welding

PICMA® multilayer actuators are produced in dierent shapesDepending on the application, they can also be

assembled with adapted ceramic or metal end pieces, additional coating, temperature sensors, etc

In the past years, the technologies or processing

actuators in an unsintered state have been conti-

nuously developed For this reason, round geometriesor PICMA® actuators with an inner hole can also be

manuactured

OF P I EzO ACtuAtORs

Manufacturing

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4


other processing and mounting steps are

similar to those or stacked PICA actuators

Pressing Technology

PICA stack actuators such as PICA Stack,

Thru or Shear consist o thin piezoceramic

plates with a standard layer thickness o

05 mm For manuacturing, piezoceramic

cylinders or blocks are shaped with pressing

technology, sintered and then separated

into plates with diamond waer saws Me-

tal electrodes are attached with thin or thick

lm methods depending on the material,

and the ceramic is then polarized

Stack actuators are created by gluing the pla-

tes together whereby a thin metal contact pla-

te is placed between each two ceramic plates

in order to contact the attached electrodes

The contact plates are connected with each

other in a soldering step, and the nished

stack is then covered with a protective poly-

mer layer and possibly an additional shrink

tubing

Picoactuator® piezo actuators consist o

crystalline layers with a thickness o 038

mm In contrast to ceramic, the orientation

o the spontaneous polarization is not deter-mined by a erroelectric polarization but by

the cutting direction in the monocrystal AllFinal inspection

Mounting and assembling technology:

Gluing, poss ultrasonic drilling or inner

hole, soldering, coating

Polarization

Application o electrodes by

screen printing or sputtering

Lapping, grinding, diamond slicing

Debindering and sintering

Pressing and shaping

Spray drying

Milling

Calcination, presintering

Mixing the raw materials

Pressing Technology

The nal processing o the piezoceramic plates manuactured with pressing technology is adapted to their

uture use The gure shows dierent piezo actuator modules

Completely assembled stack actuators with a metalendpiece and SGS expansion sensor (let), with stran-ded wires, temperature sensor and transparent FEP

shrink tubing (right)



4


PT Tube Actuators

PT Tube actuators are manuactured rom

piezoceramic cylinders that were previous-

ly produced with the pressing technologyThe outer diameter and the parallelism o

the end-surace are precisely set through

centerless circular grinding and surace

grinding The inner hole is drilled with an

ultrasonic method

The metalization then is done with thin- or

thick-layer electrodes, possibly accompa-

nied by structuring o the electrodes with a

laser ablation method

In addition to the described procedure or

manuacturing precision tubes with very

narrow geometric tolerances, the more cost-ecient extrusion method is also available

or small diameters

Structured electrodes allow specic driving o tube actuators

Laminated ceramic layers in a DuraAct transducer

arrangement (array)

Dierent shapes o DuraAct actua-tors with ceramic plates in pressing

and multilayer technology

Manufacturing of Piezo Actuators (Continued)DuraAct Patch Actuators and Transducers

DuraAct patch actuators use piezoceramic

contracting plates as their base product De-

pending on the piezoceramic thickness, the-

se plates are manuactured with pressing

technology (>02 mm) or tape technology

(005 to 02 mm) The plates are connected

to orm a composite using conductive ab-

ric layers, positioning tapes, and polyimide

cover tapes

The lamination process is done in an auto-clave in a vacuum, using an injection me-

thod This results in completely bubble-ree

laminates o the highest quality

The curing temperature prole o the auto-

clave is selected so that a dened internal

preload o the piezoceramic plates will re-

sult due to the dierent thermal expansion

coecients o the materials involved

The result o this patented technology are

robust, bendable transducer elements that

can be manuactured in large batches

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4


Properties of Piezoelectric Actuatorsd IsPlACEMEnt bEhAV IOR

Nonlinearity

The voltage-dependent displacement curves

o piezo actuators have a strongly nonlinear

course that is subject to hysteresis due to the

extrinsic domain contributions It is there-

ore not possible to interpolate linearly rom

the nominal displacement to intermediate

positions with a particular driving voltage

The electromechanical and dielectric large-

signal curves o piezo ceramics illustrate thecharacteristics (g 20) The origin o each

graph is dened by the respective thermally

depolarized condition

The shape o both bipolar large-signal cur-

ves is determined by the erroelectric po-

larity reversal process when the coercive

eld strength EC

is achieved in the opposing

eld The dielectric curve shows the very

large polarization changes at these switch-

over points At the same time, the contrac-

tion o the ceramic ater reversing the po-

larity turns into an expansion again, since

the polarization and the eld strength havethe same orientation once more This pro-

perty gives the electromechanical curve its

characteristic butterfy shape Without the

electric eld, the remnant polarizations Prem

/-Prem

and the remnant strain Srem

remain

Piezo actuators are usually driven unipolar-

ly A semibipolar operation increases the

strain amplitude while causing a stronger

nonlinearity and hysteresis which result

rom the increasing extrinsic domain por-

tions o the displacement signal (g 21)

Fig 21: Unipolar and semibipolar electromechanical

curves o erroelectric piezo ceramics and denition

o the piezoelectric large-signal deormation coeci-

ent d(GS)

as the slope between the switchover points

o a partial hysteresis curve

E

S

ΔS

ΔE

P

Ec E-Ec

Prem

unipolar

semi-bipolar

bipolar

S

EEc

Srem

unipolar

semi-bipolar

bipolar

Fig 20: Displacement o erroelectric piezo ceramics with dierent control amplitudes parallel to the

direction o polarization direction Large-signal curves as a unction o the electrical eld strength E

a) electromechanical behavior o the longitudinal strain S, b) dielectric behavior o the polarization P

In the PI and PIC data

sheets, the ree displace-

ments o the actuators are

given at nominal voltage

Piezoelectric

Deormation Coefcient

(Piezo Modulus)

The gradient ΔS/ ΔE

between the two switch-

over points o the non-linear hysteresis curves

is dened as the piezo-

electric large-signal

deormation coecients

d(GS)

(g 21) As the

progressive course o

the curves shows, these

coecients normally

increase along with the

eld amplitude (g 22)

1,5 2,00,5 1,00,0

1500

1000

500

2000

0

EPP [kV/mm

d ( G S )

[ p m / V ]

d15

PIC155 bipolar

d15

PIC255 bipolar

d33

PIC153 unipolar

d33

PIC151 unipolar

d33

PIC255 unipolar

d33

PIC252 unipolar

-d31

PIC252 unipolar

Fig 22: Piezoelectric large-signal

deormation coecients d(GS)

or

dierent materials and control mo-

des at room temperature and with

quasistatic control With very small

eld amplitudes, the values o the

coecients match the material

constants on p 36

a) b)

d(GS)

= ΔS (Equation 11)

ΔE



6


Estimation o the Expected Displacement

I the values rom g 22 are entered into the equations 3 to 10 (p 39-41), the attainable displacement at a particular

piezo voltage can be estimated The eld strength can be calculated rom the layer heights o the specic component

and the piezo voltage VPP The layer thickness o the PI Ceramic standard products can be ound starting on p 42

The ree displacement o the components that can actually be attained depends on urther actors such as the mecha-

nical preload, the temperature, the control requency, the dimensions, and the amount o passive material

Hysteresis

In open-loop, voltage-controlled operation,

the displacement curves o piezo actuators

show a strong hysteresis (Fig 24) that usu-ally rises with an increasing voltage or eld

strength Especially high values result or

shear actuators or with bipolar control The

reason or these values is the increasing in-

volvement o extrinsic polarity reversal pro-

cesses in the overall signal

Creep

Creep describes the change in the displace-

ment over time with an unchanged drive

voltage The creep speed decreases loga-rithmically over time The same material

properties that are responsible or the hys-

teresis also cause the creep behavior:

Fig 23: The hysteresis

value Hdisp

is dened as the

ratio between the maximum

opening o the curve and themaximum displacement

ΔL

V

ΔLmax

Max Diff ΔL

2,51,5 2,00,5 1,00,0

40%

35%

30%

25%

10%

15%

20%

5%

0%

EPP[kV/mm]

H d i s p

d15

PIC155 bipolar

d15

PIC255 bipolar

d33

PIC151 unipolar

d33

PIC252/255 unipolar

d33

PIC153 unipolar

Fig 24: Displacement hysteresis Hdisp

o various

actuator materials in open-loop, voltage-controlled

operation or dierent drive modes at room tempe-

rature and with quasistatic control

Fig 25: Displacement o a piezo actuator when

driven with a sudden voltage change (step unction)

The creep causes approx 1% o the displacement

change per logarithmic decade

ΔL(t) ≈ ΔL

t = 0.1s1 +γ lg ( t ) (Equation 12)

0.1s

t Time [s]

ΔL(t) Displacement as

a unction o time

[m]

ΔLt=0.1s

Displacement at

01 seconds ater

the end o the

voltage change

[m]

γ Creep actor,

depends on thematerial proper-ties (approx 001

to 002, corres-ponds to 1% to 2%per decade)

Displacement Behavior (Continued)

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4


PI oers a wide range

o position-controlled

piezo systems with

capacitive sensors or

strain gauges When the

actuator and sensor are

combined with suitable

guiding mechanics, a

low-noise amplier and

corresponding control

algorithms, these sys-tems achieve positio-

ning accuracies in the

subnanometer range

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Position Control Hysteresis and creep o piezo actuators can

be eliminated the most eectively through

position control in a closed servo loop To

build position-controlled systems, the PI Ce-

ramic piezo actuators o the PICA Stack and

PICA Power product line can be optionally

oered with applied strain gauges

In applications with a purely dynamic con-

trol, the hysteresis can be eectively redu-

ced to values o 1 to 2% even with open-loop

control by using a charge-control amplier

(p 63)

Fig 26: Elimination o hysteresis and creep in a piezo

actuator through position control



8


Below the Curie temperature, the tempera-

ture dependance o the remnant strain and

the coercive eld strength is decisive or the

temperature behavior Both the attainable

displacement with electric operation and

the dimensions o the piezoceramic element

change depending on the temperature

The cooler the piezo actuator, the greater the

remnant strain Srem

and the coercive eld

strength Erem

(g 27) The curves become

increasingly fatter with decreasing tem-

peratures This causes the strain induced by

a unipolar control to become smaller and

smaller even though the total amplitude o

the bipolar strain curve hardly changes over

wide temperature ranges The lower the

temperature, the greater the remnant strain

All in all, the piezo ceramic has a negative

thermal expansion coecient, ie the

piezo ceramic becomes longer when it cools

down In comparison: A technical ceramic

contracts with a relatively low thermal

expansion coecient upon cooling This

surprising eect is stronger, the more

completely the piezo ceramic is polarized

Displacement as a Function o the

Temperature

How much a key parameter o the piezo

actuator changes with the temperature de-pends on the distance rom the Curie tem-

perature PICMA® actuators have a relatively

high Curie temperature o 350°C At high

operating temperatures, their displacement

only changes by the actor o 005%/K

S

EEc

Srem

S

EEc

Srem

EEc

S

Srem

1000100101

100%

80%

60%

40%

20%

0%

R e l a t i v e A u s l e n k u n g

Temperatur [K]

unipolar 0 bis 120 V

bipolar -120 bis 120 V

Fig 27: Bipolar electromechanical large-signal curve o piezo actuators at dierent temperatures From let: behavior at low temperatures, at room

temperature, at high temperatures

Fig 28: Relative decrease in the displacement using

the example o a PICMA® stack actuator in the

cryogenic temperature range with dierent piezo

voltages in relation to nominal displacement at room

temperature

Properties of Piezoelectric ActuatorstEMPERAtuRE -dEPEndEnt bEhAV IOR

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4


At cryogenic temperatures, the displace-

ment decreases When controlled uni-

polarly in the liquid-helium temperature

range, piezo actuators only achieve 10 to

15% o the displacement at room tempera-

ture Considerably higher displacements at

lower temperatures can be achieved with

a bipolar drive Since the coercive eld

strength increases with cooling (g 27),

it is possible to operate the actuator with

higher voltages, even against its polariza-

tion direction

Dimension as a Function o the

Temperature

The temperature expansion coecient o

an all-ceramic PICMA® stack actuator is ap-

proximately -25 ppm/K In contrast, the ad-

ditional metal contact plates as well as the

adhesive layers in a PICA stack actuator lead

to a nonlinear characteristic with a positive

total coecient (g 29)

I a nanopositioning system is operated in

a closed servo loop, this will eliminate tem-

perature drit in addition to the nonlinearity,

hysteresis, and creep The control reserve to

be kept or this purpose, however, reduces

the usable displacement

For this reason, the temperature drit is

oten passively compensated or by a suit-

able selection o the involved materials, the

actuator types, and the system design For

example, all-ceramic PICMA® bender actua-

tors show only a minimal temperature drit

in the displacement direction due to their

symmetrical structure

Temperature Operating Range

The standard temperature operating range

o glued actuators is -20 to 85°C Selecting

piezo ceramics with high Curie temperatu-

res and suitable adhesives can increase this

range Most PICMA® multilayer products

are specied or the extended range o -40

to 150°C With special solders, the tempera-

ture range can be increased so that special

models o PICMA® actuators can be used

between -271°C and 200°C, ie, over a range

o almost 500 K

-100 -80 -60 -40 -20 0 20 40 60 80 100

-0.06

-0.04

-0.02

0.02

0.04

0.06

0.08

0

Temp. [°C]

T h e r m a l s t r a i n [ % ]

E = 1 kV/mm

no preload

Measuring sequence

PICMA® Stack

PICA Stack / PICA Power

Fig 29: Temperature expansion behavior o PICMA® and PICA actuators with electric large-

signal control



0


Preload and Load Capacity

The tensile strengths o brittle piezo ceramic

and single-crystal actuators are relatively

low, with values in the range o 5 to 10 MPa

It is thereore recommended to mechanically

preload the actuators in the installation The

preload should be selected as low as possible

According to experience, 15 MPa is sucient

to compensate or dynamic orces (p 54); in

the case o a constant load, 30 MPa should not

be exceeded

Lateral orces primarily cause shearing

stresses in short actuators In longer ac-

tuators with a larger aspect ratio, bending

stresses are also generated The sum o

both loads yield the maximum lateral load

capacities that are given or the PICA shear

actuators in the data sheet (p 24) These

values can be transerred to actuators with a

similar geometry However, it is normally re-

commended to protect the actuators against

lateral orces by using guidings

Stiness

The actuator stiness kA

is an important

parameter or calculating orce generation,

resonant requency, and system behavior

Piezoceramic stack actuators are characte-

rized by very high stiness values o up to

several hundred newtons per micrometer

The ollowing equation is used or calcula-

tion:

Bending actuators, however, have sti-

nesses o a ew newtons per millimeter,

lower by several orders o magnitude In

addition to the geometry, the actuator sti-

ness also depends on the eective elasticity

module E* Because o the mechanical depo-

larization processes, the shape o the stress-

strain curves (g 30) is similarly nonlinear

and subject to hysteresis as are the electro-

mechanical curves (g 21) In addition, the

shape o the curve depends on the respecti-

ve electrical control conditions, the drive re-quency, and the mechanical preload so that

values in a range rom 25 to 60 GPa can be

measured As a consequence, it is dicult to

dene a generally valid stiness value

For speciying piezo actuators, the quasi-

static large-signal stiness is determined

with simultaneous control with a high eld

strength or voltage and low mechanical pre-

load As a result, an unavorable operating

case is considered, ie, the actual actuator

stiness in an application is oten higher

The adhesive layers in the PICA actuatorsonly reduce the stiness slightly By using

optimized technologies, the adhesive gaps

are only a ew micrometers high so that the

large-signal stiness is only approx 10 to

20% lower than that o multilayer actuators

without adhesive layers

The actuator design has a much stronger

infuence on the total stiness, eg spheri-

cal end piece with a relatively fexible point

contact to the opposite ace

Properties of Piezoelectric ActuatorsFORCEs And st I F FnEssEs

Limitations o the Preload

The actuator begins to mechanically depolarize at only a ew tens o MPa A large-signal control repolarizes the actu-

ator; on the one hand, this causes the induced displacement to increase but on the other hand, the eective capacity

and loss values increase as well, which is detrimental to the lietime o the component

A pressure preload also partially generates tensile stress (p 64) For this reason, when very high preloads are used,

the tensile strength can locally be exceeded, resulting in a possible reduction o lietime or damage to the actuator

The amount o the possible preload is not determined by the strength o the ceramic material Piezo actuators attain

compressive strengths o more than 250 MPa

kA Stack

= E* A (Equation 13)

l

E* Eective elasticity

module: linear

increase o a

stress-strain curve

o a sample body

or actuator made

o the correspon-

ding piezoceramic

material (Fig 30)

A Actuator cross-

sectional area

l Actuator length

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5


required or this purpose amounts to the

blocking orce

Typical Load Cases

The actuator stiness kA

can be taken rom

the working graph (g 32):

It corresponds to the inverted slope o the

curve The actuator makes it possible to at-

tain any displacement/orce point on and

below the nominal voltage curve, with a

corresponding load and drive

Displacement without Preload, Load with

Low Stiness

I the piezo actuator works against a spring

orce, its induced displacement decreases

because a counterorce builds up when the

spring compresses In most applications o

piezo actuators, the eective stiness o the

load kL

is considerably lower than the sti-

ness kA

o the actuator The resulting dis-

placement ΔL is thus closer to the nominaldisplacement ΔL

0:

The displacement/orce curve in g 31 on

the right is called the working curve o the

actuator/spring system The slope o the

working curve Fe

/ ΔL corresponds to the

load stiness kL

Force Generation and Displacement

The generation o orce or displacement in

the piezo actuator can best be understood

rom the working graph (g 32) Each curve

is determined by two values, the nominal

displacement and the blocking orce

Nominal Displacement

The nominal displacement ΔL0

is specied

in the technical data o an actuator To de-

termine this value, the actuator is operated

reely, ie, without a spring preload, so that

no orce has to be produced during dis-

placement Ater the corresponding voltage

has been applied, the displacement is mea-

sured

Blocking Force

The blocking orce Fmax

is the maximum

orce produced by the actuator This orce

is achieved when the displacement o the

actuator is completely blocked, ie it works

against a load with an innitely high sti-

ness

Since such a stiness does not exist in re-

ality, the blocking orce is measured as

ollows: The actuator length beore opera-

tion is recorded The actuator is displaced

without a load to the nominal displacement

and then pushed back to the initial position

with an increasing external orce The orce

ΔS

ΔT

T

S

s m a l l

s i g n

a l

l a r g

e s i g n a l

Fig 30: Stress-strain curve o a piezoceramic stack

actuator when driven with a high eld strength, in

order to prevent mechanical depolarizations The

linear increaseΔT/ ΔS denes the eective large-

signal elasticity module E*(GS)

Small-signal values

o the elasticity modules are always greater than

large-signal values

Fig 32: Working graph o aPICMA® stack actuator withunipolar operation at dierentvoltage levels

4 0 V

2 0 V

6 0 V

8 0 V

1 0 0 V

1 2 0 V

Fmax

Δl

ΔL0

kA= Fmax (Equation 14)

ΔL0

kL

V FV

0

ΔL ΔL

ΔL0

Δl Δl

kA

kA

B

A

FF

maxF

eff

V0

0 V

kL

Δ L ≈ Δ L0

k A (Equation 15)

k A

+ k L

Fig 31: Load case with lowspring stiness without pre-load: Drawing, displacement/ voltage graph, working graphwith working curve



2


Force Generation Without Preload, Load

with High Stiness

When large orces are to be generated, the

load stiness kL

must be greater than that o

the actuator kA

(g 33):

The careul introduction o orce is espe-

cially important in this load case, since large

mechanical loads arise in the actuator Inorder to a achieve long lietime, it is impe-

rative to avoid local pull orces (p 50)

Nonlinear Load Without Preload, Opening

and Closing o a Valve

As an example o a load case in which a

nonlinear working curve arises, a valve con-

trol is sketched in g 34 The beginning o

the displacement corresponds to operation

without a load A stronger opposing orce

acts near the valve closure as a result o the

fuid fow When the valve seat is reached,

the displacement is almost completely

blocked so that only the orce increases

Large Constant Load

I a mass is applied to the actuator, the

weight orce FV

causes a compression o the

actuator

The zero position at the beginning o the

subsequent drive signal shits along the

stiness curve o the actuator No additional

orce occurs during the subsequent drive

signal change so that the working curveapproximately corresponds to the course

without preload

An example o such an application is dam-

ping the oscillations o a machine with a

great mass

Forces and Stiffnesses (Continued)

Fig 33: The actuator works without a preload against

a load with a high stiness From let: Drawing,

displacement/voltage graph, working graph withworking curve

ΔL ΔL

ΔL0

ΔL0

A B

B

A

Δl Δl

VV

0

FF

maxF

eff

V0

0 V

k L

k A

k A

k L

ΔL ΔL

ΔL0

ΔL0

A B

B

A

Δl Δl

VV

0F

maxF

eff

V0

0 VF

Fig 34: Nonlinear load without preload: Drawing,

displacement/voltage graph, working graph with

working curve

ΔL0

A B

m

B

A

Δl Δl

VV

0

F

F’

~ΔL0

Fv

ΔL’0

V0

0 V

F’max

Fig 35: Load case with large mass: Drawing,

displacement/voltage graph, working graph with

working curve

Example: The stiness considerably increases when the actuator is electrically operated with a high impedance, as is

the case with charge-control ampliers (p 63) When a mechanical load is applied, a charge is generated that cannot

fow o due to the high impedance and thereore generates a strong opposing eld which increases the stiness

F eff ≈ F

max

k L (Equation 16)

k A

+ k L

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5


Spring Preload

I the mechanical preload is applied by a re-

latively sot spring inside a case, the same

shit takes place on the stiness curve as

when a mass is applied (g 36) With a con-

trol voltage applied, however, the actuator

generates a small additional orce and the

displacement decreases somewhat in re-

lation to the case without load due to the

preload spring (Equation 15) The stiness

o the preload spring should thereore be

at least one order o magnitude lower thanthat o the actuator

Actuator Dimensioning and Energy Consi-

deration

In the case o longitudinal stack actuators,

the actuator length is the determining va-

riable or the displacement ΔL0 In the case

o nominal eld strengths o 2kV/mm, dis-

placements o 010 to 015% o the length

are achievable The cross-sectional area

determines the blocking orce Fmax

Approxi-

mately 30 N/mm² can be achieved here

The actuator volume is thus the determining

parameter or the attainable mechanical

energy Emech

=(ΔL0

Fmax

)/2

The energy amount Emech

that is converted

rom electrical to mechanical energy when

an actuator is operated corresponds to the

area underneath the curve in g 37 Howe-

ver, only a raction Eout

o this total amount

can be transerred to the mechanical load

The mechanical system is energetically opti-

mized when the area reaches its maximum

This case occurs when the load stiness

and the actuator stiness are equal Thelight blue area in the working graph corre-

sponds to this amount A longitudinal piezo

actuator can perorm approx 2 to 5 mJ/cm³

o mechanical work and a bending actuator

achieves around 10 times lower values

Efciency and Energy Balance o a Piezo

Actuator System

The calculation and optimization o the to-

tal eciency o a piezo actuator system

depends on the eciency o the amplier

electronics, the electromechanical conversi-

on, the mechanical energy transer, and the

possible energy recovery The majority o

electrical and mechanical energies are basi-

cally reactive energies that can be recovered

minus the losses, eg, rom heat generati-on This makes it possible to construct very

ecient piezo systems, especially or dyna-

mic applications

Fv

K L

A B

B

A

Δ

V FV

0

ΔL0

Δ

ΔL0

F’F’

maxF’

eff

FV

ΔL’0

V0

0 V

kL

Fig 36: Load case with spring preload: Drawing, displacement/volta-

ge graph, working graph with working curve

Fig 37: Mechanical energy amounts in the

working graph o a piezo actuator with spring

load: Emech

converted mechanical energy and

Eout

output mechanical energy

Δl

FFmax

Feff

Eout

Emech

ΔL

ΔLo



4


Properties of Piezoelectric ActuatorsdynAMIC OPERAt IOn

Resonant Frequency

The resonant requencies specied or lon-

gitudinal stack actuators apply to operation

when not clamped on both sides In an

arrangement with unilateral clamping, the

value has to be divided in hal

The reducing infuence o an additional load

on the resonant requency can be estimated

with the ollowing equation:

In positioning applications, piezo actuators

are operated considerably below the reso-

nant requency in order to keep the phase

shit between the control signal and the

displacement low The phase response o

a piezo system can be approximated by a

second order system:

How Fast Can a Piezo Actuator Expand?

Fast response behavior is a characteristic

eature o piezo actuators A ast change in

the operating voltage causes a ast position

change This behavior is desired especially

in dynamic applications, such as scanning

microscopy, image stabilization, valve con-

trols, generating shockwaves, or active vi-

bration damping When the control voltage

suddenly increases, a piezo actuator can

reach its nominal displacement in approxi-

mately one third o the period o its reso-

nant requency 0

(g 38)

In this case, a strong overshoot occurs

which can be partially compensated or with

corresponding control technology

Example: A unilaterally clamped piezo actu-

ator with a resonant requency o 0

= 10 kHz

can reach its nominal displacement in 30 µs

Dynamic Forces

With suitable drive electronics, piezo actua-tors can generate high accelerations o se-

veral ten thousand m/s² As a result o the

inertia o possible coupled masses as well

as o the actuators themselves, dynamic

pull orces occur that have to be compensa-

ted or with mechanical preloads (p 50 )

In sinusoidal operation, the maximum

orces can be estimated as ollows:

Example: The dynamic orces at 1,000 Hz,

2 µm displacement (peak-peak) and 1 kg

mass are approximately ±40 N

Tmin ≈ 1 (Equation 19)

3f 0

Fdyn ≈ ±4π2 m

rms

ΔL f 2 (Equation 20)

2

m Mass o the piezo

actuator

M Additional load

φ Phase angle [de-

gree]

f 0

Resonant requen-

cy without load

[Hz]

f 0' Resonant requen-

cy with load [Hz]

Feff

Dynamic orce [N]

meff

Eective mass o

the piezo stack

actuator [kg]

meff ' Eective mass o

the piezo stack

actuator with load

[kg]

ΔL Displacement

(peak-peak) [m]

f Control requency

[Hz]

meff ≈

m/3

M

meff ≈

m/3+M

mm

'

Fig 39: Calculation o the eective

masses me

and the me

' o a

unilaterally clamped piezo stack

actuator without and with load

φ ≈ 2 arctan f

(Equation 18)

f 0

f 0‘ =f 0 m

eff

(Equation 17)

meff ‘√

Fig 38: Displacement o an undamped piezo system ater a voltage jump The nominal

displacement is attained ater around one third o the period length

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5


Properties of Piezoelectric ActuatorsElECtR ICAl OPERAt IOn

Operating Voltage

PI Ceramic oers various types o piezo ac-

tuators with dierent layer thicknesses This

results in nominal operating voltages rom

60 V or PICMA® Bender actuators to up to

1000 V or actuators o the PICA series

Electrical Behavior

At operating requencies well below the re-

sonant requency, a piezo actuator behaves

like a capacitor The actuator displacement

is proportional to the stored electrical char-

ge, as a rst order estimate

The capacitance o the actuator depends

on the area and thickness o the ceramic as

well as the material properties In the case

o actuators that are constructed o several

ceramic layers electrically connected in pa-

rallel, the capacitance also depends on the

number o layers

In the actuators there are leakage current

losses in the µA range or below due to the

high internal resistance

Electrical Capacitance Values

The actuator capacitance values indicated

in the technical data tables are small-signal

values, ie measured at 1 V, 1,000 Hz, 20°C,

unloaded The capacitance o piezoceramics

changes with the voltage amplitude, the

temperature and the mechanical load, to

up to 200% o the unloaded, small-signal,

room-temperature value For calculations

under large-signal conditions, it is oten

sucient to add a saety actor o 70% o the

small-signal capacitance (Fig 40)

The small-signal capacitance C o a stack ac-

tuator can be estimated as or a capacitor:

With a xed actuator length l the ollowing

holds true with n ≈ l/hL:

Accordingly, a PICMA® stack actuator with

a layer thickness o 60 µm has an approx

70 times higher capacitance than a PICA

stack actuator with the same volume and

a layer thickness o 500 µm The electric

power consumption P o both types is

roughly the same due to the relationship P ~ C V 2 since the operating voltage changes

proportionally to the layer thickness

Positioning Operation, Static and with Low

Dynamics

When electrically charged, the amount o

energy stored in a piezo actuator is around

E = 1 2 CV 2 Every change in the charge (and

thereore in displacement) is connected

with a charge transport that requires the ol-

lowing current I:

Slow position changes only require a low

current To hold the position, it is only ne-

cessary to compensate or the very low

leakage currents, even in the case o very

high loads The power consumption is cor-

respondingly low

Even when suddenly disconnected rom the

electrical source, the charged actuator will

not make a sudden move The discharge

and thus the return to zero position will hap-

pen continuously and very slowly

Fig 40: Relative change o capacitance o a PICMA®

Stack actuator measured at 1 kHz unipolar sine

signal The electrical capacitance increases along

with the operating voltage and temperature

C Capacitance [C]

n Number o ceramic

layers in the actua-

tor

ε33

T Permittivity =

ε33 / ε

0(c table

p 36) [As/Vm]

A Actuator cross-sec-

tional area [m²]

l Actuator length [m]

h L

Layer thickness in

the actuator [m]

i Current [A]

Q Charge [C, As]

V Voltage on the piezo

actuator [V]

t Time [s]

Fig 41: Structure and contacting o

a stacked piezo translator

33C = n ε T

A

(Equation 21)

h L

33C = l ε T

A

(Equation 22)

h L

2

I =

dQ

= C

dV (Equation 23)

dt dt



6


Operation with Position Control

In closed-loop operation, the maximum ope-

rating requency is also limited by the phase

and amplitude response o the system Rule

o thumb: The higher the resonant requen-

cy o the mechanical system, the higher the

control bandwidth can be set The sensor

bandwidth and perormance o the cont-

roller (digital or analog, lter and controller

type, bandwidth) also limit the operating

bandwidth o the positioning system

Power Consumption o the Piezo Actuator

In dynamic applications, the power con-

sumption o the actuator increases linearly

with the requency and actuator capaci-

tance A compact piezo translator with a

load capacity o approx 100 N requires less

than 10 watt o reactive power with 1000 Hz

and 10 µm stroke, whereas a high-load

actuator (>10 kN load) requires several

100 watt under the same conditions

Heat Generation in a Piezo Element in

Dynamic OperationSince piezo actuators behave like capacitive

loads, their charge and discharge currents

increase with the operating requency The

thermal active power P generated in the ac-

tuator can be estimated as ollows:

P ≈ π

· tanδ · ƒ · C · V pp

2 (Equation 24)

4

For actuator piezoceramics under small-

signal conditions, the loss actor is on the

order o 001 to 002 This means that up to

2% o the electrical power fowing through

the actuator is converted into heat In the

case o large-signal conditions, this can in-

crease to considerably higher values (Fig

42) Thereore, the maximum operating re-

quency also depends on the permissible

operating temperature At high requencies

and voltage amplitudes, cooling measures

may be necessary For these applications,PI Ceramic also oers piezo actuators with

integrated temperature sensors to monitor

the ceramic temperature

Continuous Dynamic Operation

To be able to operate a piezo actuator at the

desired dynamics, the piezo amplier must

meet certain minimal requirements To

asses these requirements, the relationship

between amplier output current, operating

voltage o the piezo actuator, and operating

requency has to be considered

Driving with Sine Functions

The eective or average current Ia

o the

amplier specied in the data sheets is the

crucial parameter or continuous operation

with a sine wave Under the dened ambi-

ent conditions, the average current values

are guaranteed without a time limit

I a

≈ ƒ · C · V pp

(Equation 25)

Equation 26 can be used or sinusoidal

single pulses that are delivered or a short

time only The equation yields the requiredpeak current or a hal-wave The amplier

must be capable o delivering this peak cur-

rent at least or hal o a period For repeated

single pulses, the time average o the peak

currents must not exceed the permitted

average current

I max

≈ ƒ · π · C · V pp

(Equation 26)2,51,5 2,00,5 1,00,0

0,30

0,25

0,10

0,15

0,20

0,05

0,00

EPP [kV/mm]

t a n δ

PIC255 shear bipolar

PIC255 longitudinal bipolar

PIC151 longitudinal unipolar

PIC252/255 longitudinal unipolar

Fig 42: Dielectric loss actors tan δ

or dierent materials and control

modes at room temperature andwith quasistatic control The

conversion between voltage and

eld strength or specic actuators

is done with the layer thicknesses

that are given starting on p 42

The actual loss actor in the com-

ponent depends on urther actors

such as the mechanical preload,

the temperature, the control re-

quency, and the amount o passive

material

The average current, peak

current and small-signal

bandwidth or each piezo

amplier rom PI can be

ound in the technical

data

P Power that is conver-

ted into heat [W]

tan δ Dielectric loss actor

(ratio o active power

to reactive power)

f Operating requency

[Hz]

C Actuator capacitance

[F]

V pp

Driving voltage

(peak-to-peak) [V]

Electrical Operation (continued)

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5


Driving with Triangular Waveorm

Both the average current and the peak cur-

rent o the amplier are relevant or driving

a piezo actuator with a symmetrical trian-

gular waveorm The maximum operating

requency o an amplier can be estimated

as ollows:

f max

≈ 1

·

I a (Equation 27)

C V pp

A secondary constraint that applies here is

that the amplier must be capable o de-

livering at least Imax

= 2 Ia

or the charging

time, ie or hal o the period I this is not

easible, an appropriately lower maximum

operating requency should be selected For

ampliers which cannot deliver a higher

peak current or not or a sucient period o

time, the ollowing equation should be used

or calculation instead:

f max

≈

1

·

I a (Equation 28)

2 · C V pp

Signal Shape and Bandwidth

In addition to estimating the power o the

piezo amplier, assessing the small-sig-

nal bandwidth is important with all signal

shapes that deviate rom the sinusoidal

shape

The less the harmonics o the control sig-

nal are transerred, the more the resulting

shape returns to the shape o the dominant

wave, ie, the sinusoidal shape The band-

width should thereore be at least ten-old

higher than the basic requency in order to

prevent signal bias resulting rom the non-

transerred harmonics

In practice, the limit o usable requency

portions to which the mechanical piezo

system can respond is the mechanical reso-

nant requency For this reason, the electri-

cal control signal does not need to include

clearly higher requency portions

Switching Applications, Pulse-mode

Operation

The astest displacement o a piezo ac-

tuator can occur in 1/3 o the period o its

resonant requency (p 54) Response times

in the microsecond range and accelerations

o more than 10,000 g are easible, but

require particularly high peak current rom

the piezo amplier

This makes ast switching applications such

as injection valves, hydraulic valves, swit-ching relays, optical switches, and adaptive

optics possible

For charging processes with constant cur-

rent, the minimal rise time in pulse-mode

operation can be determined using the ol-

lowing equation:

t ≈ C ·

V pp (Equation 29)

I max

As beore, the small-signal bandwidth o the

amplier is crucial The rise time o the am-plier must be clearly shorter than the piezo

response time in order not to have the amp-

lier limit the displacement In practice, as a

rule-o-thumb, the bandwidth o the ampli-

er should be two- to three-old larger than

the resonance requency

Advantages and Disadvantages o Position

Control

A position control-loop always operates in

the linear control portion o voltages and

currents Since the peak current is limited in

time and is thereore nonlinear, it cannot be

used or a stable selection o control para-

meters As a result, position control limits

the bandwidth and does not allow or pulse-

mode operation as described

In switching applications, it is thereore

oten not possible to attain the necessary

positional stability and linearity by position

control Linearization can be attained eg

by means o charge-controlled ampliers

(p 63) or by numerical correction methods

Ia

average current

o the amplier

(source / sink) [A]

Imax

peak current o the

amplier (source /

sink) [A]

f operating requency

[Hz]

f max

maximum operating

requency [Hz]

C actuator capaci-

tance, large signal

[Farad (As/V)]

Vpp

driving voltage

(peak-to-peak) [V]

t time to charge piezo

actuator to Vpp

[s]

The average current and

peak current or each pi-

ezo amplier rom PI can

be ound in the technical

data

Fig 43: PICMA® actuators with pa-tented, meander-shaped external

electrodes or up to 20 A charging

current



8


Properties of Piezoelectric Actuators AMb I Ent COnd I t I Ons

Piezo actuators are suitable or operation in

very dierent, sometimes extreme ambient

conditions Inormation on use at high tem-

peratures o up to 200°C as well as in cryoge-

nic environments is ound starting on p 48

Vacuum Environment

Dielectric Stability

According to Paschen's Law, the breakdown

voltage o a gas depends on the product o

the pressure p and the electrode gap s Air

has very good insulation values at atmos-

pheric pressure and at very low pressures

The minimum breakdown voltage o 300 V

is at a ps product o 1000 Pa mm PICMA®

Stack with nominal voltages o considerably

less than 300 V can thereore be operated at

any intermediate pressure In order to pre-

vent breakdowns, PICA piezo actuators with

nominal voltages o more than 300 V, howe-

ver, should not be operated or only be driven

at strongly reduced voltages when air is in

the pressure range o 100 to 50000 Pa

Outgassing

The outgassing behavior depends on the

design and construction o the piezo actua-

tors PICMA® actuators are excellently suited

to use in ultrahigh vacuums, since they are

manuactured without polymer components

and can be baked out at up to 150°C UHV

options with minimum outgassing rates are

also oered or dierent PICA actuators

Inert Gases

Piezo actuators are suitable or use in inert

gases such as helium, argon, or neon Howe-

ver, the pressure-dependent fashover resis-tances o the Paschen curves must also be

observed here as well The ceramic-insulated

PICMA® actuators are recommended or this

use, since their nominal voltage is below the

minimum breakdown voltages o all inert ga-

ses For PICA actuators with higher nominal

voltages, the operating voltage should be

decreased in particular pressure ranges to

reduce the fashover risk

Magnetic Fields

Piezo actuators are excellently suited to be

used in very high magnetic elds, eg, at

cryogenic temperatures as well PICMA®

actuators are manuactured completely

without erromagnetic materials PICA stack

actuators are optionally available without

erromagnetic components Residual mag-

netisms in the range o a ew nanotesla have

been measured or these products

Gamma Radiation

PICMA® actuators can also be operated in

high-energy, short-wave radiation, which oc-

curs, or example, with electron accelerators

In long-term tests, problem-ree use with

total doses o 2 megagray has been proven

Environments with High Humidity

When piezo actuators are operated in dry

environments, their lietime is always

higher than in high humidity When the

actuators are operated with high-requency

alternating voltages, they sel-heat, thus kee-

ping the local moisture very low

Continuous operation at high DC-voltages in

a damp environment can damage piezo actu-

ators (p 59) This especially holds true or the

actuators o the PICA series, since their active

electrodes are only protected by a polymer

coating that can be penetrated by humidity

The actuators o the PICMA® series have an

all-ceramic insulation, which considerab-

ly improves their lietime in damp ambient

conditions compared to polymer-coated

actuators (p 59)

Liquids

Encapsulated PICMA® or specially encased

PICA actuators are available or use in

liquids For all other actuator types, direct

contact with liquids should be avoided

Highly insulating liquids can be exceptions to

this rule Normally, however, the compatibili-

ty o the actuators with these liquids must be

checked in lietime tests

In case o questions regar-

ding use in special envi-

ronments, please contact

ino@piceramiccom

http://www.p/

http://www.p/



5


Lietime when Exposed to DC-Voltage

In nanopositioning applications, constant

voltages are usually applied to the piezo

actuator or extended periods o time In

the DC operating mode, the lietime is in-

fuenced mainly by atmospheric humidity

I the humidity and voltage values are very

high, chemical reactions can occur and

release hydrogen molecules which then de-

stroy the ceramic composite by embrittling

it

All-Ceramic Protective Layer

The patented PICMA® design suppresses

these reactions eectively In contrast to

coating made just o polymer, the inorga-

nic ceramic protective layer (p 42) prevents

the internal electrodes rom being exposed

to water molecules and thus increases the

lietime by several orders o magnitude (g

43)

Quasi-static Conditions: Accelerated Lie-

time Test

Due to their high reliability, it is virtually

impossible to experimentally determine

the lietime o PICMA® actuators under real

application conditions Thereore, tests un-

der extreme load conditions are used to

estimate the lietime: Elevated atmospheric

humidity and simultaneously high ambient

temperatures and control voltages

Fig 44 shows the results o a test that was

conducted at a much increased atmospheric

humidity o 90% RH at 100 V DC and 22°C

The extrapolated mean lietime (MTTF,

mean time to ailure) o PICMA® actuatorsamounts to more than 400,000 h (approx

47 years) while comparative actuators with

polymer coating have an MTTF o only

approx one month under these conditions

Tests under near-realistic conditions con-

rm or even surpass these results

Calculation o the Lietime when Exposed

to DC-Voltage

Elaborate investigations have been done

to develop a model or calculation o the

lietime o PICMA® Stack actuators The ol-

lowing actors need to be taken into account

under actual application conditions: Ambi-

ent temperature, relative atmospheric humi-

dity, and applied voltage

The simple ormula

MTTF = AU

· AT

· AF (Equation 30)

allows the quick estimation o the average

lietime in hours The actors AU

as a unc-

tion o the operating voltage, AT

or the am-

bient temperature and AF

or the relative

atmospheric humidity can be read rom the

diagram (g 45)

REl IAb I l I ty OF P ICMA ® Mult I lAyER ACtuAtORs

Properties of Piezoelectric Actuators

Fig 44: Results o an accelerated lietime test with increased humidity (test conditions:

PICMA® Stack and polymer-coated actuators, dimensions: 5 x 5 x 18 mm³, 100 V DC, 22 °C,

90% RH)

Important: Decreasing

voltage values are asso-ciated with exponential

increases o the lietime

The expected lietime at

80 V DC, or example, is

10 times higher than at

100 V DC

This calculation can also

be used to optimize a

new application with

regard to lietime as

early as in the design

phase A decrease in

the driving voltage orcontrol o tempera-

ture and atmospheric

humidity by protective

air or encapsulation o

the actuator can be very

important in this regard



0


Lietime in Dynamic Continuous Operation

Cyclic loads with a rapidly alternating elec-

trical eld and high control voltages (typi-

cally > 50 Hz; > 50 V) are common conditions

or applications such as valves or pumps

Piezo actuators can reach extremely high

cycles-to-ailure under these conditions

The most important actors aecting the

lietime o piezo actuators in this context are

the electrical voltage and the shape o the

signal The impact o the humidity, on the

other hand, is negligible because it is redu-

ced locally by the warming-up o the piezo

ceramic

Ready or Industrial Application: 10 10

Operating Cycles

Tests with very high control requencies de-

monstrate the robustness o PICMA® piezo

actuators Preloaded PICMA® actuators with

dimensions o 5 x 5 x 36 mm were loaded at

room temperature and compressed air coo-ling with a sinusoidal signal o 120 V unipo-

lar voltage at 1,157 Hz, which corresponds

to 108 cycles daily Even ater more than 1010

cycles, there was not a single ailure and the

actuators showed no signicant changes in

displacement

Patented Design Reduces the Mechanical

Stress

PICMA® actuators utilize a special paten-

ted design Slots on the sides eectively

prevent excessive increases o mechanical

tensile stresses in the passive regions o

the stack and the ormation o un-controlled

cracks (g 46) that may lead to electrical

breakdowns and thus damage to the actu-

ator Furthermore, the patented meander-

shaped design o the external contact strips

(g 43) ensures all internal electrodes have

a stable electrical contact even at extreme

dynamic loads

Reliability of PICMA® Multilayer Actuators (Continued)

Fig 46: The patented PICMA®

actuator design with its dened

slots preventing uncontrolled

cracking due to stretching upon

dynamic control is clearly visible

Fig 45: Diagram or calculati-

on o the lietime o PICMA®

stack actuators when exposed

to DC-voltage For continuous

operation at 100 V DC and 75%

relative humidity (RH) and an

ambient temperature o 45°C,

the ollowing values can be

read rom the diagram: AF=14

(humidity, blue curve), AT=100

(temperature, red curve), and

AU=75 (operating voltage,

black curve) The product

results in a mean lietime o

105,000 h, more than 11 years

http://www.p/

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6


Piezo Electronics for Operating Piezo ActuatorsChARACtER Ist IC bEhAV IOR OF P I EzO AMPl I F I ERs

Fast settling or slow speed with high con-

stancy, high positional stability, high resolution

and high dynamics – the requirements placed

on piezo systems vary greatly and need a

control with a high degree o fexibility

The control electronics play a key role in the

perormance o piezoelectric actuators and

nanopositioning systems Ultra-low-noise,

high-stability linear ampliers are essential

or precise positioning, because piezo actua-

tors respond to the smallest changes in the

control voltage with a displacement Noise

or driting must be avoided as much as pos-

sible The prerequisite or the high-dynamics

displacement o the actuator is or the voltage

source to provide sucient current to charge

the capacitance

Power Requirements or Piezo Operation

The operating limit o an amplier with a

given piezo actuator depends on the amplier

power, the amplier design and the capaci-

tance o the piezo ceramics (c p 56–57) In

high-dynamics applications, piezo actuators

require high charge and discharge currentsThe peak current is o special importance,

particularly or sinusoidal operation or pulse

operation Piezo ampliers rom PI are there-

ore designed so that they can output and sink

high peak currents I an amplier is operated

with a capacitive load and requency at which

it can no longer produce the required current,

the output signal will be distorted As a

result, the ull displacement can no longer be

attained

Amplifer Frequency Response Curve

The operating limits o each amplier modelare measured with dierent piezo loads de-

pending on the requency and output volta-

ge and are graphically displayed as amplier

response curves to make the selection easier

The measurements are perormed ater 15

minutes o continuous operation (piezo and

amplier) at room temperature In cold condi-

tion ater power up, more power can be brie-

ly available

The power amplier operates linearly within

its operating limits so that the control signal

is amplied without distortion In particular,

no thermal limitation takes place, ie the am-

plier does not overheat, which could cause

distortions o the sine wave The amplier

continuously provides the output voltage

even over a long time This amplier respon-

se curve cannot be used or peak values that

are only available or a short period

The curves reer to open-loop operation; in

closed-loop operation, other actors limit the

dynamics

Setting the Operating Voltage

Ater the operating limit o the amplier has

been reached, the amplitude o the opera-

ting voltage must be reduced by the same

proportion as the output voltage alls, i the

requencies continue to increase This is

important because the current require-

ment continuously increases along with the

requency Otherwise, the output signal will

be distorted

Example: The E-503 (E-663) amplier can

operate a 23 µF piezo capacitance with

an output voltage o 100 V and a maximum

requency o approximately 15 Hz (with sine

wave excitation) At higher requencies the

operating limit decreases, e g to 80 V at

20 Hz In order to obtain a distortion-ree

output signal at this requency, the control

input voltage must be reduced to 8 V (voltage

gain = 10)

Fig 47: Amplier requency

response curve, determined with

dierent piezo loads, capacitance

values in µF Control signal sine,

operation period > 15 min, 20° C

Here: E-617, a switched amplier

with energy recovery



2


Piezo Electronics for Operating Piezo ActuatorssOlut IOns FOR h Igh -dynAMICs 24/7 OPERAt IOn

Switching Amplifers with Energy

Recovery

Piezo actuators are oten used or an es-

pecially precise materials processing, or

example in mechanical engineering or ne

positioning in milling and turning machines

These require high orces as well as dyna-

mics The piezo actuators are correspon-

dingly dimensioned or high orces; ie

piezo actuators with a high capacitance are

used here Particularly high currents are

required to charge and discharge them with

the necessary dynamics The control o

valves also requires similar properties

Energy Recovery Minimizes the Energy

Consumption in Continuous Operation

Since these applications requently run

around the clock, seven days a week, the

energy consumption o the amplier is

particularly important For this purpose,

PI oers switching amplier electronics

with which the pulse width o the control

signal is modulated (PWM) and the piezo

voltage is thereby controlled This resultsin an especially high eciency In addition,

a patented circuitry or energy recovery is

integrated: this stores part o the returning

energy in a capacitive store when a piezo is

discharged and makes the energy available

again or the next charging operation This

permits energy savings o up to 80% to be

realized Furthermore, the amplier does

not heat up so much and thus infuences the

actual application less

Unlike conventional class D switching

ampliers, PI switching ampliers or

piezo elements are current- and voltage-

controlled Product examples are the E-617or PICMA® actuators (p 29) and E-481 or

the PICA actuator series (p 31)

Protection o the Piezo Actuator through

Overtemperature Protection

In continuous operation, the heat develop-

ment in the piezo actuator is not negligible

(p 56) Corresponding electronics can there-

ore evaluate the signals o a temperature

sensor on the piezo This protects the cera-

mic rom overheating and depolarization

Valid patents

German patent no 19825210C2International patent no 1080502B1

US patent no 6617754B1

Fig 48: Piezo actuator in a case

with connections or temperature

sensor and cooling air

0

20

40

60

80

100

0 20 40 60 80 100

E f f i c i e n c y i n %

Output power, relative to max. in %

Switching amplifier Linear amplifier

0,00

5,00

10,00

15,00

20,00

25,00

0 500 1000 1500 2000

P o w e r c o n s u m

p t i o n i n W

Frequency in Hz

Linear amplifier

Switching amplif ier

Fig 49: Thanks to their patented energy recovery system, PI

ampliers only consume approx 20% o the power required

by a corresponding linear amplier with the same output

power

Fig 50: Power consumption o a piezo amplier with linear and

switching amplier at the piezo output, capacitive load 1 µF The

measured values clearly show that the pulse width modulated amplier

allows signicantly higher dynamics than the classic linear amplier

The linear amplier reaches the upper limit o its power consumption

at requencies o up to approx 700 Hz, the switching amplier does not

reach the limit until ar beyond 2 kHz

http://www.p/

http://www.p/



6


Piezo Electronics for Operating Piezo Actuatorsl InEAR IzEd AMPl I F I ERs FOR P I EzO d IsPlACEMEnt wIthOut hystEREs Is

Charge Control

A typical application or piezo actuators

or nanopositioning systems is dynamic

scanning This involves two dierent

methods: step-and-settle operation with

precise and repeatable position control on

the one hand, and ramp operation with

especially linear piezo displacement on the

other The rst method requires a closed

servo loop which ensures that positions

can be approached precisely and repeatedly

with constant step sizes

O course, ramp operation with linear piezo

displacement is also possible using position

eedback sensors and a servo loop How-

ever, in this case, the servo loop will

determine the dynamics o the entire sys-

tem which sometimes signicantly limits

the number o cycles per time unit This

can be avoided by means o an alternative

method o amplication: charge control

Charge and Displacement

Charge control is based on the principle that

the displacement o piezo actuators is much

more linear when an electrical charge is ap-

plied instead o a voltage The hysteresis is

only 2% with electrical charges, whereas it

is between 10 and 15% with open-loop con-

trol voltages (g 51) Thereore, charge con-

trol can oten be used to reach the required

precision even without servo loop This en-

hances the dynamics and reduces the costs

Charge control is not only o advantage asregards highly dynamic applications but

also when it comes to operation at very low

requencies However, charge control is not

suitable or applications where positions

need to be maintained or a longer period

o time

Fig 51: Typical expansion o piezo actuators in relation to the applied voltage (let) and the

charge (right) Controlling the applied charge signicantly reduces the hysteresis

ΔV

Δl

Q

Δl

For dynamic applica-

tions:

Active vibration

damping

Adaptronics

High-speed mechanical

switches

Valve control (eg

pneumatics)

Dispensing

The charge-controlled E-50610 power amplier oers highly linear,

dynamic control or PICMA® piezo actuators



4


Handling

Piezo actuators are subject to high mechani-

cal and electrical loads Moreover, the brittle

ceramic or crystalline materials require

careul handling

Avoid mechanical shocks to the actuator,

which can occur during alls, or example

Do not use metal tools during installation

Avoid scratching the ceramic or polymer

coating and the end suraces during ins-

tallation and use

Prevent the ceramic or polymer insulation

rom coming into contact with conductive

liquids (such as sweat) as well as metal

dust

I the actuator is operated in a vacuum:

Observe the inormation on the per-

missible piezo voltages in particular pres-

sure ranges (p 58)

I the actuator can come into contact with

insulating liquids such as silicone or hyd-

raulic oils, contact ino@piceramicde

I the actuator has accidently become dir-

ty, careully clean the actuator with isop-

ropanol or ethanol beore putting it back

into operation Next, completely dry it in

a drying cabinet Never use acetone or

cleaning When cleaning in an ultrasonic

bath, reduce the energy input to the ne-

cessary minimum

Recommendation: Wear gloves and

protective glasses during installation and

start-up

DuraAct patch actuators and encapsulated

PICMA® piezo actuators have a particularly

robust construction They are partially

exempt rom this general handling inorma-

tion

Mechanical Installation (g 52, 53, 54)

Avoid torques and lateral orces whenmounting and operating the actuator by

using suitable structures or guides

When the actuator is operated dynami-

cally: Install the actuator so that the center

o mass o the moving system coincides

with the actuator axis, and use a guiding

or very large masses

Establish contact over as large an area as

possible on the end suraces o a stack

actuator

Select opposing suraces with an even-

ness o only a ew micrometers

Gluing

I the mounting surace is not even, use

epoxy resin adhesives or gluing the

actuator Cold-curing, two-component

adhesives are well suited or reducing

thermo-mechanical stresses

Maintain the operating temperature

range specied or the actuator during

hardening and observe the temperature

expansion coecients o the involved

materials

Uneven mounting suraces are ound, or

example, with PICMA® Bender and PICMA®

Chip actuators, since these suraces are not

re-ground ater sintering (g 55)

. . :

. . :. . :

Fig 52: Avoiding lateral orces and

torques

Fig 54: Avoiding tensile stresses

by means o a mechanical preload

Fig 55: Mounting by gluing o a one-sidedly

clamped bending actuator

Fig 53: Prevention o torques

OF P I EzO ACtuAtORs

http://www.p/

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6


Applying a Preload (fg. 54)

Create the preload either externally in

the mechanical structure or internally in

a case

Apply the preload near the axis within the

core cross-section o the actuator

I the actuator is dynamically operated and

the preload is created with a spring: Use

a spring whose total stiness is approxi-

mately one order o magnitude less than

that o the actuator

Introducing the Load Evenly (fg. 56)

The parallelism tolerances o the mecha-

nical system and the actuator result in an

irregular load distribution Thereore, com-

pressive stresses may cause tensile stresses

in the actuator As regards the even appli-

cation o the load, there are dierent de-

sign solutions that dier rom each other in

terms o the axial stiness, the separability

o the connection as well as the rotatability

in operation, eg in the case o lever ampli-

cation Gluing the actuator (p 64, Gluing section)

Hardened spherical end piece with point

contact to even opposing surace

Hardened spherical end piece with ring

contact to a spherical cap

Connection via a fexure joint

I the actuator is coupled in a milling po-

cket, make sure that there is ull-area con-

tact on the end surace o the actuator For

this purpose, select the dimensions o the

milling pocket correspondingly or make

ree cuts in the milling pocket (Fig 57)

I a point load is applied to the end piece

o the actuator: Dimension the end piece

so that its thickness corresponds to hal

the cross-sectional dimension in order to

prevent tensile stresses on the actuator

(g 58)

Electrical Connection (g 59)

From an electrical point o view, piezo

actuators are capacitors that can store a

great amount o energy Their high internal

resistances lead to very slow discharges

with time constants in the range o hoursMechanical or thermal loads electrically

charge the actuator

Connect the case or the surrounding me-

chanics to a protective earth conductor in

accordance with the standards

Electrically insulate the actuator against

the peripheral mechanics At the same

time, observe the legal regulations or the

respective application

Observe the polarity o the actuator du-

ring connection

Only mount the actuator when it is short-

circuited

When the actuator has charged: Dis-

charge the actuator in a controlled

manner with a 10 kΩ resistance Avoid

directly short-circuiting the terminals o

the actuator

Do not pull out the connecting cable to

the amplier when voltage is present

The mechanical impulse triggered by this

could damage the actuator

Sae Operation

Reduce the DC voltage as much as

possible during operation o the actuator

(p 59) You can decrease oset voltages

with semibipolar operation

Always switch o the actuator when it is

not needed

Avoid steep edges in the piezo voltage,

since they can trigger strong dynamic

orces when the actuator does not have

a preload Steep edges can occur, or

example, when digital wave generators

are switched on

Tensile

stresses

Tensile

stresses

Fig 56: Avoiding an irregular load application

Fig 57: Full-area contact o the

actuator

Fig 58: Proper dimensioning o

the end pieces in the case o point

contact

Fig 59: Mechanical loads electri-

cally charge the actuator Moun-

ting only when short-circuited



6


PI (Physik Instrumente) is the leading supplier

o piezo-based positioning systems with accu-

racies in the range o a ew nanometers.

The extensive product portfolio is based on a

wide range of technologies with electromotive

or piezoelectric drives for up to six motion axes.

Hexapods, nanometer sensors, control electro-

nics as well as software and are supplemented

by customized solutions.

All key technologies are developed in-house.

This means that every phase from the design

right down to the shipment can be controlled:

The precision mechanics and the electronics as

well as the position sensors and the piezo cera-

mics or actuators. The latter are produced by

the subsidiary company PI Ceramic.

PI is, therefore, the only manufacturer of nano-

positioning technology which employs the

piezoelectric drives it produces. This ensures a

high degree of flexibility for developing custo-

mized piezoceramic components.

More than 100 patents and patents applied for

stand for more than 40 years of experience and

pioneering work. PI products are employed

wherever technology in industry and research

is pushed forward – worldwide.

With four German factories and ten subsidiaries

and sales offices abroad, the PI group is repre-

sented internationally.

PI stands for quality in products, processes and

service. The ISO-9001 certification, which focu-

ses not only on product quality but also on

customer expectations and satisfaction, was

achieved back in 1994.

PI is also certified according to the ISO 14001

(environmental management) and OHSAS

18001 (occupational safety) standards, which

taken together form an Integrated Manage-

ment System (IMS).

Future Technology

Solutions

Today PI delivers micro-

and nanopositioning solu-

tions or all important

high-tech markets:

n Semiconductor technology

n Optical metrology,

microscopy

n Biotechnology and

medical devices

n Precision automation

and handling

n Precision machining

n Data storage technology

n Photonics, tele-

communications

n Nanotechnology

n Micropositioning

n Aviation and aerospace

n Astronomy

FOR IndustRy And REsEARCh

Drives that Set the World in Motion

http://www.p/

http://www.p/


http://slidepdf.com/reader/full/piezoelectric-effect-piezo-techlology-tutorial-pi-ceramic 35/38P I E z O t E Ch nO l O g y

1970 PI founding year

1977 PI headquarters move to Waldbronn,

Germany

1987 Foundation of a subsidiary in the USA

1991 Foundation of a subsidiary in Japan

1991 Market launch of 6-axis parallel-

kinematics positioning systems

(Hexapods)

1992 Foundation of PI Ceramic, Thuringia,

Germany; crucial step towards market

leadership in nanopositioning

1993 Foundation of subsidiaries in the UK

and in France

1994 Market launch of capacitive position

sensors

1995 Foundation of a subsidiary in Italy

1998 Market launch of digital control

electronics

2001 Market launch of PILine® Ultrasonic

Piezomotors

2001 New company building in Karlsruhe,

Germany

2002 PI Ceramic company building extended

2002 Foundation of a subsidiary in China

2002 Market launch of PICMA® multilayer

Piezo stack actuators

2004 Market launch of NEXLINE® high-

performance piezo linear drives

2007 Market launch of NEXACT® piezo

linear drives

2010 Acquisition of the expansion site next

to the PI headquarters

2011 Foundation of a subsidiary in Korea

2011 Foundation of a subsidiary in Singapore

2011 Acquisition of the majority shares of

miCos GmbH

2012 Extension of the buildings in Karlsruhe

and Lederhose

A s u C C E s s s t O R y

Milestones

6



8


I I I II I I I

I I I II I I I

I I I II I I I

nAnOPOsIt IOnIng systEMs, MICROPOsIt IOnIng

tEChnOlOgy & nAnOMEtROlOgy

Product Portfolio

Nanopositioning

Resolution Down to Picometers

Nanopositioning systems achieve motion resolu-tions and positioning accuracy in the nanometerrange and below The target position is achievedwithin a ew milliseconds and stably maintainedPiezo actuators or piezo stepping drives are usedas drives Digital motion controllers optimize theperormance o the system These systems arerequired in optical metrology, microscopy, or inmicrochip production To achieve the necessaryposition resolution and stability, PI manuacturesand develops the sensor systems and oers theseas an independent product line

From linear axes to motion in 6

degrees o reedom

Parallel-kinematic principle or multi-

axis systems

Versions with direct position mea-

surement

– capacitive sensors:

Subnanometer resolution

– Incremental sensors: Nanometer

resolution, wide measurement

ranges

Available in a variety o designs,

travel ranges, and precision classes

PiezoWalk® Stepping Drives

Precise Positioning over Several Millimeters

Piezo stepping drives transer the advantages o conventional piezo actuators to applications withlarger travel ranges The interplay o the motion

o individual actuators brings about a walk mo-tion with high resolution and dynamics within asingle step and thus, in principle, allows unlimi-ted travel ranges The actuators are prestressedagainst the moving slider The drive is thereoresel-locking when switched o without holdingcurrents or additional mechanical componentsThere is thereore no heat dissipation or controldither, the position is maintained with a high de-gree o stability

Two principles:

– NEXLINE®: Generated orce up to

600 N

– NEXACT®: Fast motion and gene-

rated orce up to 10 N

Integration levels rom an economi-

cal OEM drive to a multi-axis positio-

ning system

Compact design, variable travel due

to variable rod length

Nanometer resolution

Vacuum compatible and non-

magnetic

PILine® Ultrasonic Piezomotors

Small and Fast over Long Distances

Ultrasonic piezomotors are an alternative to theconventional motor spindle combinations or tomagnetic drives and allow outstandingly fat po-sitioning systems They oer excellent start/stopdynamics, high velocity and sel-locking in a smallpackage PI supplies miniaturized versions, OEMmotors and drives, and also complete positioningsystems with controller Piezomotors rom PI arevacuum-compatible in principle and suitable oroperation under strong magnetic elds

Integration levels rom an economi-

cal OEM drive to a multi-axis positio-

ning system Flexible travel ranges

Easy mechanical integration

Sel-locking at rest

Holding orce to 15 N

Velocity to 500 mm/s

http://www.p/

http://www.p/



6


Hexapods - Parallel-Kinematic Positioning

Systems

High-Precision Motion Control in up to Six Axes

PI uses parallel-kinematic designs wherever mul-ti-axis and high-precision motion is required Alldrives act directly on the same moving platormThis creates advantages in the precision anddynamics compared to stacked axes, where theerrors o the individual axes are cumulative anddynamic losses are caused because the upperaxes are also carried along The parallel-kinema-tic principle is independent o the drive used Itis thus possible to produce micropositioning andnanopositioning systems with motion in up to sixdegrees o reedom

Low moving mass, low inertia

Excellent dynamic behavior, ast

step-and-settle

Small installation space

High stiness

Freely denable pivot point

Minimized axis crosstalk motion

Very good repeatability

For all drive systems

High resolution D/A and A/D con-

verters, state o the art processor

technology

Digital real-time interaces

Extensive sotware and drivers

Inormation on coordinates or

parallel kinematics/Hexapods

Digital Control Technology

Achieve the Optimum in Perormance

The perormance characteristics o a precisionpositioning system depend equally on the stagemechanics and the control Digital controllers use

specially adapted algorithms to process processvalues such as sensor signal or position target va-lue Motions on trajectories, settling times, or tra-jectory deviations can thus be optimized duringast scanning operations

Linear positioners

– Travel ranges between 5 and

1000 mm– Velocity to 150 mm/s

– Low-cost designs, variants as

modular system

DC and stepper micrometer drives

– Travel ranges to 50 mm and veloci-

ty to 30 mm/s

– Resolution to <100 nm

Rotary stage with unlimited slewing

range

– to 720 °/s

– Resolution to 1 µrad

– ncremental encoders or direct po-

sition measurement as an optional

extra

Micropositioning

Precision Positioning over Long Travel

Micropositioning systems provide motion reso-lution and positioning accuracies in the rangebetween a ew tens o micrometers and 01 µmBrushless DC or stepper motors are available asdrives, as well as linear drives such as PILine® ul-trasonic piezomotors or NEXACT® piezo steppingdrives The precision o the system depends onthe integrated drive, position sensor, and guidesIn conventional motors, the quality o the gear,the spindle, or the worm drive play also an essen-tial role Digital controls with suitable control andlinearization methods make it possible to improvethe system characteristics



P I E Z O N A N O P O S I T I O N I N G

JAPAN

PI Japan Co., Ltd.TachikawaBusiness Center Bldg. 5F2-38-5 Akebono-choTachikawa-shi, Tokyo 190-0012Tel. +81 (42) 526 7300Fax +81 (42) 526 [email protected]

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